The present disclosure relates to an optical semiconductor apparatus.
For example, an optical semiconductor apparatus where semiconductor laser devices having different emission wavelengths are integrated is known as a wavelength-tunable light source used for DWDM (Dense Wavelength Division Multiplexing) optical communication and the like. In such an optical semiconductor apparatus where semiconductor laser devices are integrated, generally, an optical coupling unit and the semiconductor laser devices are integrated on the same substrate. The optical coupling unit combines laser light beams output from the semiconductor laser devices. The combined laser light is output from the optical semiconductor apparatus.
At this point in time, suppose that the optical coupling unit integrated in the optical semiconductor apparatus is one without wavelength selectivity such as a multimode interferometer (MMI: Multi Mode Interferometer) optical coupler, the output optical power of the optical semiconductor apparatus with respect to the output optical power of the semiconductor laser devices is equal to or less than a factor of the number of the integrated semiconductor laser devices. Therefore, a loss is high.
Hence, in order to reduce the loss and increase the output efficiency of the device, an optical semiconductor apparatus using an arrayed waveguide grating (AWG: Arrayed Waveguide Grating) as the optical coupling unit is known (see, for example, Japanese Laid-open Patent Publication No. 2008-282937). The AWG includes an input slab waveguide, a waveguide array, and an output slab waveguide. The AWG uses the diffraction phenomenon caused by an optical path difference of the waveguide array to have a similar effect to the diffraction grating.
However, if an AWG and semiconductor laser devices having different wavelengths are combined for use, the loss characteristics of the AWG and the gain characteristics of the semiconductor laser device are multiplied. Accordingly, there is a problem that it is difficult to increase the optical power of laser light at a band edge.
The AWG has a characteristic that the loss (coupling loss) is the lowest at the central wavelength and the loss increases farther away from the central wavelength. On the other hand, the semiconductor laser device is generally designed such that the gain of the active layer is the largest around the central wavelength. Accordingly, the gain decreases farther away from the central wavelength. As a result, there arises a situation where although the gain of the active layer of the semiconductor laser device at the band edge is low, the loss of laser light at the band edge is also high in the AWG. As a result, if an attempt is made to increase the power of the optical semiconductor apparatus, a power limit at the band edge where the disadvantageous conditions result in being linked restricts power over the entire band by the method of the known technology.